1. Unit 2.3 Robust Programs Lesson 2 - Testing Programs

2. Starter
For each letter of the Alphabet write down one test that begins with that letter.
For example
D Driving Test
G GCSE exam

3. Learning Objectives Understand the purpose of testing
Identify different types of program errors
Know the difference between iterative and terminal testing
Be able to select suitable test data

4. Key Words Iterative testing Final/terminal testing Syntax Errors
Logic errors
Test Data

5. Program errors, what is the worst that could happen?

6. Programs errors What errors have you come across?
Could the Heartbleed have bee avoided?
Who is responsible for the Heartbleed bug?

7. The Twitter bug http://www.bbc.co.uk/news/technology-35361150
Discuss this article

8. What is a Error An error in a program is sometimes called a Bug
This is because Grace Hopper discovered a moth in a computer which was stopping it from functioning correctly.

9. What is a Error
Bugs cause the program to run incorrectly and are usually caused by an error in the coding
Not all errors will stop a program from running

10. Activity Look at the code on the following slide
There are some errors/bugs
Can you identify what they are.
Check with another student and compare to see if you have found them all.

11. Debug this Pseudocode There are three errors
number 1 = input(“Please enter a number”)
number 2 = input (“Please enter another number)
Sum = number 1 / numBer 2
print (Summ)

12. Activity 1 - Answer number 1 = input(“Please enter a number”)
number 2 = input (“Please Enter another number”)
Sum = number 1 / number 2
print (Summ)

13. Runtime errors
Runtime errors are errors which may cause program errors or the computer to crash even if there appears to be nothing wrong with the program code.
They are only detected once the program is executed
Examples could be: Running out of memory

14. Syntax Errors
Syntax errors are mistakes in the way that the code is written.
Translators can only execute a program if it is syntactically correct.
Common syntax errors include:
spelling mistakes
incorrect use of punctuation
-use of capital letters

15. Logic Errors
Logic errors: a logic error is a bug in a program that causes it to operate incorrectly, but not to terminate or crash.  
A logic error produces unintended or undesired output or other behaviour, although it may not immediately be recognised.

16. Activity 2
Look back at the code from the previous task and consider each error.
Classify them as either Syntax or Logic errors. Make sure you can justify your answer.

17. Activity 2 – Identify and define the errors for dividing two numbers
number 1 = input(“Please enter a number”)
output 2 = input (“Please enter another number”)
Sum = number 1 * Number 2
print (sum)

18. Activity 2 - Answer number 1 = input(“Please enter a number”)
output 2 = input (“Please enter another number”) SYNTAX
Sum = number 1 * Number 2 LOGIC AND SYNTAX
print (sum)SYNTAX

19. Types of Testing
Iterative testing is testing the code as you create it.
This could completed line by line or a section at a time.
Once tested and feedback is received you then alter your code as required.
You could consider this type of testing similar to tuning a guitar.
You keep playing the string and adjusting the tension until the note is the correct pitch.

20. Types of Testing
Final or Terminal testing is carried out at the end of the program when it has been written.
This is more similar to the GCSEs which are taken at the end of the term.
It is used to check what happens when a range of predefined test data is entered or used in the program

21. Selecting and using Suitable Test Data
When testing the program it is important to use a range of test data
valid/in range
out of range
boundary value
null value
invalid

22. Selecting and using Suitable Test Data
Valid – Data that is correct
In Range – The maximum values of the data that could be entered for example for teenagers
Out of Range – Values higher or lower than the expect range, for teenagers greater than 19
Null Value – when no data is entered or left blank to test what happens.
Invalid - incorrect values such as entering ‘Dave’ in an age field.

23. Test Plans Testing is often completed in a test plan which sets out
The test number
The data entered
The type of test data
The expected outcome
The result of the test
Action required as a result of the test

25. Key Words Recap Iterative testing Final/terminal testing Syntax Errors
Logic errors
Test Data

26. Plenary
Share with another students three new elements that you have learnt this lesson
Open a program that you have written and test it for errors.
Identify the errors in term so f syntax or logic
Create an example of a logic error in a programing language of your choice

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